Personally, I'm deliberately on the "S" upgrade cycle. I started off with a 3GS, then got a 4S, and now have a 5S. I figure I'll let other people deal with the bleeding edge, and I can get the model with all the refinements afterwards. I'd be willing to bet that a lot of other people think the same way. I don't doubt that the 6 will sell really well, probably better than the 5S, but it may not sell vastly better than the 5S.